Nix documentation using non-existent config option

[RedEtherbloom]

Describe the Issue
The documentation for how to run KoboldCpp under NixOS uses a non-existent config option, nixpkgs.config.cudaArches
How to reproduce:

1. Add NixOS example configuration from KoboldCpp Nix documentation to configuration.nix
2. Rebuild System
3. Attempt to run KoboldCpp with FlashAttention(a feature requiring a higher arch than the lowest default cudaArch for Nix, "sm_60" iirc)
   Result:
   KoboldCpp crashes due to it being compiled with sm_60, instead of sm_75 as specified:
   ggml/src/ggml-cuda/template-instances/../fattn-wmma-f16.cuh:422: ERROR: CUDA kernel flash_attn_ext_f16 has no device code compatible with CUDA arch 600. ggml-cuda.cu was compiled for: 600

Additional Information:
GPU: Nvidia GeForce RTX 2070 Super
System Information:

 - system: `"x86_64-linux"`
 - host os: `Linux 6.12.12, NixOS, 25.05 (Warbler), 25.05.20250204.799ba5b`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Lix, like Nix) 2.92.0
System type: x86_64-linux
Additional system types: aarch64-linux, i686-linux
Features: gc, signed-caches
System configuration file: /etc/nix/nix.conf
User configuration files: REDACTED
Store directory: /nix/store
State directory: /nix/var/nix
Data directory: /nix/store/9vcw1xs4znwaf01mjr7zd3zcxr173qyl-lix-2.92.0/share`
 - channels(root): `""`
 - nixpkgs: `/nix/store/k8nkf470zpidpa5nh76lh2x6rxfzpwa4-source

Potential solutions:

1. Override the cudaArch that koboldcpp is supposed to be built with, either in package list or in overlay:
   koboldcpp.override { cudaArches = ["sm_75"]; }
2. Set cudaCapabilities:
   nixpkgs.config.cudaCapabilities = ["7.5"];

[LostRuins]

Pinging @DontEatOreo

[RedEtherbloom]

Update: Both solutions have now been tested locally and seem to resolve this

[RedEtherbloom]

Ping @DontEatOreo

[DontEatOreo]

Sorry for the delay! I've had a bunch of other notifications and this slipped
through; I'll take a look